1. Field of the Invention
The present invention relates to a cellular phone equipped with a charging function, and in particular to a cellular phone equipped with a charging function that can correctly measure a charging current.
2. Description of the Related Art
Recent cellular phones are characterized by the compact size of main body and compact peripheral accessories. A charging circuit among the peripheral accessories is generally incorporated into a cellular phone main body and is recharged only when connected to an external power source via a connector.
FIG. 4 shows a block diagram of a general cellular phone equipped with a charging function. In FIG. 4, an external power source 1 is means for receiving power from an external source and is connected to a charging adapter, a charging stand, a car-mounted connector, or such. A rechargeable battery 2 is a lithium-ion battery, a nickel-hydrogen battery, or such. A charging current detector circuit 3 is means for monitoring a voltage across resistors and detecting a corresponding current value. A charging switch 4 is means for adjusting a charging current by xe2x80x9conxe2x80x9d, xe2x80x9chalf-onxe2x80x9d, and xe2x80x9coffxe2x80x9d operations. A regulator 5 is means for converting a voltage from the external power source 1 or the rechargeable battery 2 to an optimum operating voltage and supplying the operating voltage to a CPU 6 and a load 7-1. The load 7-1 is a receiver circuit, a transmitter circuit, and a synthesizer circuit, or such. The CPU 6 is means for controlling the charging current based on the current value monitored by the charging current detector circuit 3 and the voltage and type of the rechargeable battery 2. A load 7-2 is a backlight for an LCD and keys.
Operation of the related art cellular phone equipped with a charging function will be described. In charging, the charging switch 4 is in the on or half-on state. In the meantime a current flows through the charging current detector circuit 3 to charge the rechargeable battery 2. The external power source 1 is used as a power supply for operation of a cellular phone such as making calls, and supplied to each section though the regulator 5. In this practice, the current is also supplied to each section via the charging current detector circuit 3. When recharging is complete, the charging switch 4 is turned off and the rechargeable battery 2 is used as a power supply for the cellular phone.
In general, in a cellular phone equipped with a charging function, a detected current, which flow through the charging current detector circuit, is variable when the cellular phone is operated during charging. It is caused of that all of operating current occurred by the operation also flow through the charging current detector circuit. Therefore, the CPU must discriminate the current operating state of the cellular phone and correct the current value accordingly, such as subtracting the current consumed by the cellular phone from the charging current. Nevertheless, it is quite cumbersome to perform the correction since a cellular phone is operated in various operating modes. When the recharging is about to complete, the current consumption of the cellular phone is much larger than the charging current, thus causing a larger error in the detected current. As a result, a related cellular phone equipped with a charging function has a problem that the charging current cannot be measured correctly.
The invention aims to solve the aforementioned problem and to provide a cellular phone in which a current flowing in a charging current detector circuit stays constant and a charging current is detected correctly even when the cellular phone is operated during recharging.
In order to solve the problems, the invention provides a cellular phone equipped with a charging function including means for connecting to an external power source, a rechargeable battery, a charging current detector circuit and a regulator for converting a voltage from the external power source or the rechargeable battery to an optimum voltage. In the cellular phone, the charging current detector circuit is connected between the rechargeable battery and the regulator and that the external power source is connected between the regulator and the charging current detector circuit. With this configuration, a current flowing in the charging current detector circuit stays constant even when the cellular phone is operated during recharging, thereby correctly detecting the charging current.
Besides, one end of the charging current detector circuit is connected the rechargeable battery alone. With this configuration, it is not necessary to correct the detected charging current thus simplifying the charging control means.
The cellular phone further includes a charging switch for controlling a charging current. The charging switch is provided between the charging current detector circuit and the rechargeable battery or between the external power source and the charging current detector circuit. With each of the configurations, it is possible to avoid discharge of the rechargeable battery until the external power source is removed.
Moreover, the cellular phone further includes an external power detector circuit for detecting a power fed from the external power source and a short circuit for short-circuiting the charging current detector circuit when the external power detector circuit does not detect a power fed from an external power source. With this configuration, it is possible to eliminate a power loss caused by the charging current detector circuit.
Additionally, The cellular phone further includes a load having at least a backlight circuit. The load is connected between the external power source and the regulator. With this configuration, it is possible to reject the change of charging current caused by the load variation. (for example backlight on and off)